Oily wastewater streams are generated at many different refinery processing units and discharged to a refinery wastewater treatment system where treatment by gravity separation and dissolved air flotation generates oily solid streams. These oily solid wastes are regulated under the Resource, Conservation, and Recovery Act (RCRA) as listed hazardous wastes. Additionally, sludge from leaded product tanks, slop oil emulsion solids, and heat exchanger bundle solids are considered listed hazardous waste. These sludges as a group are typically 4-6% solids and 15-20% oil as generated. 15,000 to 20,000 gal/day are generated at a typical petroleum refinery.
Many refineries currently deliquify these wastes and either land dispose or land treat the remaining solids. However, the 1984 Amendments to RCRA required the Environmental Protection Agency (EPA) to identify and promulgate a system of pretreatment of all hazardous wastes prior to land disposal or land treatment. EPA's choice of pretreatment was required to be based on the best demonstrated available technology and was required by Congress to be in effect by Aug. 8, 1988 for petroleum refinery wastes. If EPA did not meet this deadline, the legislative "hammer" would be the automatic prohibition of land disposal for the waste in question. This prohibition would take effect May 8, 1990. Various technologies for treating listed hazardous refinery oil sludges to render them delistable or acceptable for land disposal under the RCRA landban have been suggested, but none have been found to be entirely satisfactory.
U.S. Pat. No. 4,311,561 discloses an apparatus and method for extracting bitumen from tar sand wherein the tar sand and a solvent flow in one direction through a plurality of interconnected individually sealed extraction chambers with the flow of extracted bitumen and solvent counter to the flow of tar sand and solvent. The solvents identified as being useful are hexane, pentane, benzene, halogenated liquids and xylene. The amount of bitumen in the tar sand is progressively reduced from reaction chamber to reaction chamber until the final chamber where sand and solvent alone are treated with hot water to remove the solvent and then discharge pure sand.
U.S. Pat. No. 4,434,028 discloses an apparatus and process for removing oil and other organic constituents from particulate, inorganic-rich mineral solids (e.g., oil-contaminated drill cuttings) using an extractant that is in a gaseous state at atmospheric pressure and ambient temperature and is converted to a liquid or supercritical fluid during the extraction process. The process involves the steps of: separating the drill cuttings from a drilling mud in a separator; slurrying the cuttings using an oil or aqueous liquid in a slurry tank; conveying the slurry to an extractor column; circulating liquefied extractant through the extractor column in contact with the drill cuttings until the desired level of oil is extracted; advancing the extractant-oil mixture from the extractor column through a pressure reduction valve to a separator-evaporator wherein the extractant-oil mixture separates into two phases, one being an extractant phase and the other being an oil-enriched phase. The extractant phase is recirculated to the extractor column. The oil-enriched phase is subjected to subsequent separations wherein the extractant is separated from the oil. Upon completion of the extraction cycle, a water piston is advanced through the extractor column to remove remaining oil and extractant from the drill cuttings. Water is then added to the clean drill cuttings to form a slurry in the extractor column which is removed and disposed of or further treated.
There is a need for efficient, economical and reliable apparatus and processes for separating undesirable organics from solid wastes, hazardous wastes, and the like, to render the product solids delistable or acceptable for land disposal. It would be advantageous if these apparatus and processes were adaptable to separating extractable organic materials from other compositions wherein such extractable organic materials are intermixed with solids and/or water.